(a) Field of the Invention
The invention relates to local area network technology, particularly to wireless local area network technology.
(b) Description of the Related Art
In general, in the application of a wireless local area network (WLAN), in order to reduce power consumption, the wireless station (STA) will enter a power-saving mode during the time interval without actual signal transmitting or receiving and return to a normal mode within a pre-determined period to receive the signal from the access point (AP). If there is no data transmitting or receiving requested by the access point, then the STA enters the power-saving mode again until the next period.
In the normal mode, the STA performs receiving or transmitting function with a high frequency clock (usually in MHz range); and in the power-saving mode, in order to reduce power consumption, the wireless station usually operates with a low frequency clock (usually in KHz range). Although the frequency of the low frequency clock is low, accuracy is still required. If the normal mode is initiated too early, power consumption will increase. If the normal mode is initiated too late, the signal from the WLAN AP will be missed to result in connection failure. In general, in order to keep the accuracy of the low frequency clock of the power-saving mode, the STA needs to utilize an external oscillator for supplying a stable and accurate clock signal to the STA, such as a 32.768 KHz clock signal. The external oscillator is independent on the environment factors, such as manufacturing process, operational voltage, temperature, and so forth. However, such the external oscillator will increase production cost.